CS208106B2 - Flexible contact lens and method of making the same - Google Patents

Description

(54) Flexible contact lens and method of manufacture thereof

The present invention relates to a flexible contact lens and to a process for its manufacture. Contact flexible lenses are well known. There are several types.

One of the first flexible contact lenses was made of a hydroxyethyl methalkylate based material, commonly referred to as HEMA, with a strength structure. This material is obtained by absorbing a significant amount of water, which is usually 35 to 75% by weight based on the amount of the base material, i.e., the methyl methacrylate. Due to their structure, hydro-based materials are often sensitive to the pH value of a tear liquid and can easily tear. Moreover, their highly hydrophilic structure makes them less resistant to biological contamination, which is virtually impossible.

A second type of contact lens, made of a silioon polymer, has been described in French Patent Specification No. 1,265,077 of August 16, 1960.

Silicone polymers of this type are substantially lipophilic and have well-known hydrophobic properties. In order for these polymers to obtain the specific mechanical resistance necessary for their practical use, a certain amount of inorganic substance, such as silica, must be added to them. However, said inorganic substance additive makes it very difficult to obtain an accurate refractive index of the material in the manufacture of lenses suitable for correcting asthism. In addition, the pronounced hydrophobic nature of these materials, which results in insufficient wetting of the surface of the silicone polymer contact lens, causes tear film tearing. Said tearing of the tear film causes irritation and therefore results in a reduction in the time for which such a contact lens can be worn comfortably and safely.

The problem of the surface wettability of silicone polymer contact lenses is solved in French Patent No. 1,526,934, dated December 1, 1966. This solution consists in making the silicone polymer hydrophilic by grafting on polyvinylpyrrolidone, commonly referred to as PVP.

Although this grafting method has certain advantages, it will not achieve completely satisfactory results, especially since the tear film has different characteristics in different oaob · Cornea is a living tissue that must be protected against abrasion; otherwise, it is irritated or even at risk of permanent damage. · The cornea normally exudes the liquid that covers it and thus reduces any abrasion by objects such as contact lenses resting on it. It should also be considered that this liquid layer forms a film which, in addition to performing an anti-abrasive function, must be maintained intact to ensure good vision without distortion.

In addition, the liquid layer or tear film fulfills many other functions relating to the cornea, such as the elimination of impurities, the transport of oxygen and the provision of electrolytic equilibrium. Since this liquid layer performs a number of functions, its character is individual, especially in terms of the amount of its aqueous and lipidic component.

Of course, it is desirable to provide a contact lens having hydrophilic and lipophobic properties to prevent tear film break in most individuals. With a lens of this nature, it would be possible to extend its wearing time, reduce eye irritation and achieve better vision by eliminating or substantially reducing the distortion caused by tear film interruption.

It is an object of the present invention to provide a flexible contact lens having hydrophilic and lipophobic properties that would eliminate or at least substantially reduce the risk of tear film interruption and hence achieve tear film continuity and increase wearing time without corneal irritation; furthermore, said lens should have a refractive index readily adaptable to astigmatism correction.

It is also an object of the present invention to provide a method for producing said lenses.

SUMMARY OF THE INVENTION The present invention provides a flexible contact lens having a generally concave-convex shape and adapted to be worn on the cornea, comprising a cross-linked graft copolymer of silicone and polyvinylpyrrolidone, said copolymer comprising from 75 to 99 wt. % of silicone and 1 to 25 wt.%, polyvinylpyrrolidone, and water containing 1 to 25 wt. Preferably, said lens has a refractive index of 1.39 to 1.45.

The present invention also relates to a process for the manufacture of said contact lens, in which a silicone polymer is prepared in a manner known per se, which is formed to form a substrate that is irradiated in an oxidizing medium, and contacted with a graft containing a substantial portion monomer to form a graft copolymer, wherein the graft copolymer is irradiated in that the graft copolymer is exposed to an atmosphere substantially de-oxygenated with ultraviolet light at a wavelength of 253.7 nm and an intensity of 10θ W / m ² for 4 to 16 hours, preferably for 8 hours, to achieve a total irradiation dose of 0.1.10 µg to 20. JO ** Gy.

The difference in wettability of the lens of the invention in which the graft polymer is crosslinked and the contact lenses known hitherto can be specified as follows:

1. Crude silicone is very lipophilic and has substantially hydrophobic properties;

2. The crosslinked silicone-polyvinylpyrrolidone copolymer has very good hydrophilic properties and limited lipophilic properties. Improvement of the hydrophilic properties is achieved due to the ability of the grafted polyvinylpyrrolidone to absorb water.

3. If the graft copolymer of silicone and polyvinylpyrrolidone is crosslinked according to the invention, then it has hydrophilic and lipophilic properties. However, the enhancement of the grafted polyvinylpyrrolidone of the invention slightly deteriorates its hydrophilic properties, although it does not modify its wettability but substantially improves its lipophilic properties. The resulting properties of course depend on the degree of crosslinking.

The molding of the contact lens according to the invention can be performed by molding in a matrix system. One such method is described in French Patent No. 2,109,470 of October 19, 1970.

The lens of the invention has a generally concave-convex shape and is adapted to swim on the cornea to which it adheres by means of the tear film described above.

The present invention also relates to a process for the production of the above-described lens according to the invention, in which the molded silicone substrate is irradiated in a known manner and then grafted with N-vinylpyrrolidone monomer to form a graft copolymer of silicone resin and polyvinylpyrrolidone. then the graft copolymer is irradiated to crosslink the graft polyvinylpyrrolidone.

The phases of this procedure are illustrated schematically by the attached diagram.

The crosslinked material then has the desired wettability. For example, a possible method of preparing a finished lens is to prepare a silicone prepolymer mixture, which is then degassed to eliminate dissolved gases, and the degassed prepolymer is introduced into a mold where it is polymerized to form a shaped substrate, whereupon the substrate is irradiated in an oxidizing medium, the irradiated substrate is introduced into a graft medium containing N-vinylpyrrolidone monomer to form a graft copolymer, then the graft copolymer of silicone and polyvinylpyrrolidone irradiates the graft polyvinylpyrrolidone according to the invention.

This second irradiation, which causes crosslinking of the grafted polyvinylpyrrolidone chains, produces a shaped lens having the hydrophilic and lipophobic properties described above.

Before use, the lens thus produced is immersed in a solution that is close to a tear liquid, such as a physiological saline solution.

Silicone substrates are generally obtained by crosslinking, with platinum-containing catalysts, suitable mixtures of organopolysiloxanes which are substituted with a predominant amount of non-unsaturated hydrocarbon groups and less aliphatic unsaturated groups; in addition, some of these organopolysiloxanes include hydrogen atoms attached to silicon atoms.

Such mixtures may consist, for example, of:

1. 100 parts of diorganopolysiloxane of the following general formula:

R RR l II

CH ₀ = CHSi (SiO) _{M 9} SiCH = CH ² I I.

R Y in which R and R ', which are identical or different, represent alkyl groups of 8 with a total number of carbon atoms of 1 to 4, such as methyl, ethyl, propyl and butyl, aryl groups with a total number of carbon atoms of 6 to 8 such as for example phenyl, tolyl and л

208106 4 xylyl, wherein at least 50% of R * is methyl and n is any number having a value such that the viscosity of diorganopolysiloxane is 300 to 800,000 cPo at 25 ° C, preferably 500 to 200,000 cPo at 25 ° G.

2. 5 to 50 parts of a copolymer consisting of the components of formulas (R'1SiOq, (R **) CH _o = CHS10 _{q Л} and 2 3 -a and SiO ₂ , in which R, which are identical or different, represent alkyl groups having the total number of carbon atoms 1 to 3, such as methyl, ethyl and propyl, and the symbol a denotes 1 or 2, wherein the ratio of the number of (R) ₃ SiO ₂ and and the copolymer contains 1.5 to 3.5 weight percent vinyl groups.

3.

Hydrogenenoorganopolysiloxane of the general formula

in an amount sufficient to provide 0.8 to 1.9 binding of SiH per binding of SiCH 3 CH 3 ratios

1 and 2, wherein R * is as defined above, b is any number from 0.6 to 2, c is any number from 0.3 to 1, and 1 mole of hydrogenopolysiloxane contains at least two SiH bonds .

4. Catalyst based on platinum.

The preparation of mixtures of this type is described in more detail in U.S. Patent No. 3,436,366 and in further U.S. Patent No. 3,284,406.

As an illustrative example of compositions particularly suitable for the preparation of the contact lenses of the present invention, compositions comprising:

- 100 parts of a diorganopolysiloxane oil of formula (CH ₃ ) ₂ CH ₂ = CHSiO [Si (CH ₃ ) ₂ 1 _n -S1CH = CH ₂ (CH ₃ ) ₂ , in which n * is such that the oil viscosity is 500 up to 5,000 cPo at 25 ° C;

- 25 to 40 parts of a copolymer formed by the components of the formulas (CH ^ J ^ SÍOq (CH ₃₎ CH ₂ = CHSi and SiO _2, wherein the ratio of components (CH3) ₃ SiO _{Q 5,} and (CH ₃₎ CH ₂ = CHS1O к the number of SiO ₂ components is 0.6 / 1 to 1/1;

- hydrogenomethylpolysiloxane of the average formula <SiO. _Л .4.7b_r.c 2 • in an amount sufficient к obtain 0.9 to 1.7 SiH bonds for one bond SiCH = _CH2 preceding two polymers, wherein in said general formula the symbol b 'is any number from 0.9 to 1.6 and c * is any number from 0.45 to 0.85;

0.0009 to 0.005 parts of platinum in a solvent soluble form, such as an alkanol having a total carbon number of 1 to 15.

These mixtures are preferably subjected to a pressure lower than atmospheric pressure at a temperature of from 15 to 60 ° C to remove gases and low molecular products contained therein. The mixtures are then placed in suitable molds where they are heated at 80 to 160 ° C for 1 to 5 hours. During this time, the mixtures cured to silicone elastomers. The substrate thus obtained is then removed from the mold and irradiated with ionizing radiation. Any type of ionizing radiation is suitable for this purpose, provided that the silicone substrate does not degrade to the extent that the Sy Syls severely impair its optical properties. Thus, SYT gamma irradiation from a source of Co ^ ⁰ as x-rays or radiation ultrfiaaoového buoOsadování electrons přččeež důležžté is that the radiation induced ionization time subssrátu. This irradiation is carried out in the presence of an oxidizing medium, such as, for example, pure oxygen, air or an oxidizing solution, preferably in the atherogenic oxygen. The radiation dose is preferably equal to 0,1.10 ptWtžrš ^ Gy ^and 2 Gy ^{4 0} .10. ^D AVK this price ^y ^ can be achieved no time variations and ^p ^^ oizity ex ozice with jedirým constraints, namely that the optical properties are maintained with ^ t ^ s ^ s ^ pentaene.

The irradiated substrates, which are ready for grafting, can be maintained at a temperature of 0 ° C for a long time in this irradiated state.

Oxygen is then removed from the substrate which has been irradiated and from the grafting medium by, for example, the method described in French Patent No. 1,526,934, which has already been used.

Snubs ^! Thus, contact is made with the grafting medium containing a significant amount of N-vioylpyrrolidone monomer in the pure state or in solution. Before the irradiated substrate is brought into contact with the grafting medium, it is possible to heat said sub-substrate up to a temperature of about 250 ° C, but the grafting reaction also takes place at ambient temperature.

If the substrate is thickened, it is preferable to heat the substrate to a temperature in the range of about 120 ° C to 200 ° C. Under these conditions, the grafting reaction is easily initiated. The time for which the substrate is maintained in contact with said monomer may be from 15 minutes to 2 hours. The graft substrate is then washed and dried in an oven.

The basic component of the grafting medium is an N-voylpyrrolidone monomer, and it is advantageous to add small polyvoylpyrrolidone up to about 5% by weight and / or small amount. up to about 5% by weight of a monoosine surfactant such as a blocky allyl silicone polyolefin copolymer selected from the group of copolymers described on pages 373-376 of W. NoHa ChemOssry and Tedmology et al.

Illustrative examples of these copolymers are branched or linear copolymers I and II corresponding to the formulas:

СНз | ³

I. (C ^^ SiLoSiC ^^ HS, 8 [Si] (CH ₂ ) ₃ 0 (C ₂ H ₄ 0) _{26 (} (C ₂ O ₆ ) ₂₅ ^ 10CCH 3 ^ OSKC ^^

II. CH ₃ Si [o (Si, CH ₃ ' ₂ O)

6.6'W> 4.3 ^(C 3 ^H 6 ^O > 3 ^C 4 ^H 9 ⁾ 3 ·

If the small polymerized polyvinylpyrrolidone and / or the small surfactant is used, the formation of craters and other geometric deformations is prevented, while at the same time the sieve mesh, i.e., the irradiated mesh, is improved. , grafting environment. While these additives are not necessary, it is nevertheless preferred.

The N-voylpyrrolidone monomer and the polyrinylpyrrolidone derived therefrom are prepared by well known classical methods.

In order to ensure good purity, the N-nitrophenylpyridine is pre-sterilized. When polyvinylpyrrolidone is used as an additive, the polyvinylpyrrolidone is an unfractionated product obtained by polymerizing the above monomer in a 40% aqueous solution. This polymer has a degree of K / 30 and a molecular weight of almost 40,000. The monomer is used in the grafting medium either in a pure, undiluted state or in aqueous solutions, the concentration of which ranges from about 50% by weight of monomer upwards.

Depending on the temperature used, the time, the type of irradiation and the concentration of the grafting medium, the grafting of said substrate may lead either to a homogeneously grafted copolymer or to a product grafted only on the surface.

For example, irradiation with an increased dose of from 0.1 to about 20 megarads and grafting in pure monomer with or without the above ingredients for 0.1 to 8 hours and at a temperature of about 120 to 200 ° C results in a copolymer that is homogeneous throughout the substrate.

The grafting degree can be determined by simply weighing the starting product and the grafting product.

A preferred composition is about 75 to 99% silicone polymer and about 1 to 25% graft polyvinylpyrrolidone.

It is contemplated that irradiation of the substrate in the presence of an oxidizing environment induces the formation of peroxide centers in the silicone substrate. Once contacted with the N-vinylpyrrolidone monomer, these centers react to form a graft copolymer. Due to vinyl groups, the N-vinylpyrrolidone monomer reacts mainly with peroxydic centers on silicone

If the monomer reacts to itself to a small extent (homopolymer formation), only linear or branched polymers are produced, but not crosslinked.

The crosslinking according to the invention is carried out on a graft substrate.

A cross-linking agent such as 5% hydroxyethyl methacrylate or diethylene glycol dimethacrylate can be used for this purpose.

However, these enhancers do not give as satisfactory results as the second irradiation.

In the second irradiation, the same irradiation source as previously described may be used, with the same limitations, although for example only 8, that the second irradiation is performed in an inert atmosphere. For example, an ultraviolet radiation generator having an intensity of λ.W / m @ 2 and a wavelength of 253.7 nm is suitable for this purpose, but other sources of radiation may also be used.

When using the aforementioned generator, it is suitable to irradiate for 4 to 16 hours to achieve the desired crosslinking.

In order to obtain products having different lipophobic characteristics, different radiation sources of different intensities and varying irradiation times are used.

The total dose of irradiation has a decisive effect on the cross-linking: as already mentioned, this dose is preferably equal to 0.1.10 ^ Gy to 20.10 ^ Gy.

It is believed that crosslinking occurs mainly between the silicon grafted polyvinylpyrrolidone chains.

With increasing cross-linking, the graft copolymer, which is normally very hydrophilic, somewhat less hydrophilic and more lipophilic, becomes a result of which the properties of the resulting product can be varied by the degree of cross-linking.

With respect to the refractive index of the crosslinked graft copolymer, the ratio of silicone to polyvinylpyrrolidone which is present in the copolymer varies depending on the mofecularones.

Silicone has a refractive index of 1.42 and polyvinylpyrrolidone has a refractive index of 1.51. The finished lens has a refractive index that depends on the ratio of the components. In the case of use, do the lenses intensify? It has vodyИ i JW δ δ® n bww f water. The water index is 1.33; this index proportionally contributes to the overall refractive index of the lens. Lenses having a refractive index of between 1.39 and 1.45 can be obtained in a suitable manner.

The lowest of these indices is particularly suitable for astgmatism correcting lenses.

A silicon lens to which, for example, silica has been added, has a higher refractive index, making it less effective for correcting asthmatism.

The graft copolymers are more or less opalescent in the dry state. Transparency of these copolymers can be achieved by immersion in water.

An important property of a contact lens is its oxygen and carbon dioxide permeability, both of which are gases. it must have access to the cornea and be evallocated from there.

It has been noted that the novel cross-linked graft polymer of the present invention retains substantially the significant permeability typically associated with silcones. This gas permeability is generally expressed in cubic centimeters of gas transported by cm ² of 1 cm thick maaerial film at a differential pressure of 1.33 kPa, measured at 25 ° C, within one second. This permeability can be evaluated as a coefficient of selectivity, which is the permeability of carbon dioxide divided by the permeability of oxygen.

Permeability P ^: rm ^ (^ lectivity 02 / CO2 RTV silicone alone 94.10-9 390.10-9 4,5 10% dry copolymer 54.1O‘9 250.10-9 4.6 10% hydrated copolymer 28.10-9 190.10-9 6.8 16% dry copolymer 53,5.10-9 240.10-9 4,5 16% hydrated copolymer 36.10-9 235.1o-9 6.5

The permeability, which facilitates gas exchange on the cornea and ensures particularly good oxidation, varies relatively little depending on the grafting step used and is important for values of about 7 to 10, which are advantageous in the process according to the invention.

In the following examples, the invention is described in more detail.

All details of the amount given in the description and in the definition of the subject matter of the invention are hmoonoot unless otherwise stated.

The results of the examples are summarized in the table following these examples.

Example 1

An organopolysiloxane composition comprising the following components is used:

- 78 g of a dimethylpolysiloxane oil blocked at each end of the component of the formula _{(CH3) 2 CH2} = CHSi _0í5 with viscosity 2000 cafter at 25 ° C;

25 grams of a copolymer consisting of the components of formulas (CH ₃ ) ₃ S ₁₀ q (CH ₃ ) CH ₂ = CHSiO and SiO ₂ in a number ratio of 2.3 / 0.4 / 3.5;

- 5,5 grams of a copolymer consisting of the formulas (CH ₃ ) ₂ HSiOq of 2/1 a and SiO ₂ in Numeric

- 0.001 grams of platinum in a form soluble in octyl alcohol.

Thus, a mold having a generally concave-convex shape and whose swelling substantially reproduces the shape of the cornea is filled with said degassed mixture, the mold is closed and clamped. The temperature is raised to 120 ° C and maintained at this value for three hours to achieve silicone polymerization. The 36 mg silicone substrate is then removed from the mold and exposed to air in the presence of air at a dose of 3 * 10 &lt; 6 &gt; Thereafter, oxygen is removed from the irradiated substrate and the grafting monomer consisting of N-vinylpyrrolidone and 5% Plaston K by nitrogen. The whole is then heated to 130 ° C for 15 minutes. The graft copolymer weighed 39.2 mg after washing and drying and thus received 3.2 mg of polyvinylpyrrolidone. The graft substrate is then swollen in water and exposed to an ultraviolet generator providing 3.10 [mu] W / m &lt; 2 &gt; and a wavelength of 253.7 nm for two hours, then stored in a wet state ready for use. Weighing revealed that it retained 3.3 mg of water, which is expressed as a percentage of 8.4%.

Example 2

The substrate was prepared in exactly the same manner as in Example 1. The total weight of the silicone was 39.9 mg. The grafting is carried out as in Example 1, wherein the grafted substrate has a weight of 43.5 mg, which means that it has received 3.6 mg of polyvinylpyrrolidone. The crosslinking is carried out as in Example 1, except that the irradiation time is 4 hours.

Example 3

The procedure of Example 1 is followed except that the weight of the silicone substrate is 40 mg, while the weight of the grafted substrate is 43.5 mg. The second irradiation is also carried out as in Example 1 or 2, except that the irradiation time is 8 hours.

Example 4

The procedure was as in Example 1, except that the silicone weight was 39.7 mg, the graft weight was 43.3, and the second irradiation time was 16 hours.

Example 5

The procedure is as in Example 1, except that the weight of the silicone is 36.9 mg, the weight of the graft substrate is 40.1 mg, and the second irradiation is not performed.

Table

Example Silicone (mg) Total mass PVP (mg) PVP grafting rate (%) Water absorption Water / PVP ratio Second irradiation time (hours) mg % 1 36 39.2 3.2 8.9 3.3 3.4 1, 03 2 2 39.9 43.5 3.6 9.05 3.6 3.3 1 »oo 4 3 40 43.5 3.5 8.75 3.1 7.15 0.89 8 4 39.7 43.3 3.6 3.1 7.15 0.86 16 5 36.9 40.1 3.2 8.7 3.4 8.5 1.06 0

The table shows that the non-crosslinking material of example 5 absorbs much more water than the crosslinking samples, i.e., the samples of embodiments 1 to 4. Also, it is noted that between 8 and With 16 hours of irradiation, there is very little difference in the water / PVP ratio. The preferred irradiation time can thus be 8 hours.

In all cases lenses having a refractive index of 1.39 to 1.45 in the wet state are obtained.

Generally, the amount of water absorbed is close to the weight of the grafted PVP and is therefore preferably in the range of 1 to 25% by weight.

Claims (3)

SUBJECT OF THE INVENTION CLAIMS 1. A flexible contact lens having a generally concave-convex shape and adapted to be worn on the cornea, characterized in that it consists of a cross-linked graft copolymer of silicone and polyvinylpyrrolidone, said copolymer comprising 75 to 99% by weight of silicone and 1- 25% by weight, polyvinylpyrrolidone and water containing 1 to 25% by weight of the lens; 2. The flexible contact lens of claim 1 wherein the refractive index is from 1.39 to 1.45. 3. The process for producing a flexible contact lens according to items 1 and 2, wherein a silicone polymer is prepared in a manner known per se, which is formed to form a substrate that is irradiated in an oxidizing medium, and then contacted with a grafting medium containing a substantial N-vinylpyrrolidone monomer to form a graft copolymer, characterized in that said graft copolymer is crosslinked, by irradiating said graft copolymer in a substantially oxygen-free atmosphere with ultraviolet light at a wavelength of 253.7 nm and an intensity of 3.10θ W / m ^ for a period of 4 to 16 hours, preferably for 8 hours, to achieve a total irradiation dose of 0.1 to 20.10 Gy.